Hi Ralf,
Ralf Wildenhues <ralf.wildenh...@gmx.de> writes:
> * Ludovic Courtès wrote on Tue, Jul 20, 2010 at 06:28:46PM CEST:
>> Background: Guile 1.9/2.0 has an auto-compilation feature whereby if a
>> source file has no corresponding object file in the search path, or if
>> the object file is older than the source file, then the source file is
>> automatically recompiled and stored in ~/.cache/guile/ccache.
>
> I assume this part has nothing to do with Automake per se, right?
Right.
>> Packages that use Guile can also choose to pre-compile all their source
>> files and install both the source and object files. This saves the need
>> for users to auto-compile the source. (This is what Guile does with its
>> own source files.)
>
> I assume this, too, is currently done without help of Automake, or make,
> for that matter.
Correct.
>> For this to work, we need “make install” to guarantee the relation
>> mtime(installed-object) >= mtime(installed-source), assuming we have
>> mtime(builddir-object) >= mtime(srcdir-source), which will always be the
>> case unless the computer’s clock is skewed.
>>
>> Do Automake-generated makefiles provide such a guarantee? Regardless of
>> the ‘make’ implementation, OS, etc.?
>
> This is actually a tough question; it has little to do with Automake,
> much more with any or all of make, tar, cp, touch, install, libc, file
> system, and the kernel.
>
> `info Autoconf --index timestamp' leads to two nodes describing some of
> the problems with time stamps. The gist is that in the worst case, any
> of the above tools independently may have full or only limited timestamp
> resolution (nowadays that would mostly be either nanosecond or 1 second).
> Even well-run software distributions without user-compiled tools
> typically can't afford to (or don't) update all of these tools at once.
Indeed. Thanks for the pointer.
[...]
> Anyway, most of the time, these issues can be worked around, for example
> by sleeping for a second before building builddir objects, or between
> installing sources and installing object files, depending on whether
> install -C is used or not.
The latter would be faster IIUC (sleep 1 second instead of N seconds,
with N the number of source files.)
The ‘install’ command is chosen by Automake or the user-specified
$INSTALL, so we can’t really determine whether it uses ‘-C’, right?
> Hope that helps. It might be a bit tricky or ugly to actually put this
> sleep command in a normal automake Makefile.am, so if you know what
> exactly you need, we can create an example.
A typical Makefile.am looks like this:
--8<---------------cut here---------------start------------->8---
dist_foobar_SOURCES = foo.scm bar.scm
nodist_foobar_DATA = foo.go bar.go
.scm.go:
guile-tools compile -o $@ $<
--8<---------------cut here---------------end--------------->8---
Actually we currently have this hook, which Andy added some time ago
(here $(moddir) contains installed source files and $(ccachedir) is for
installed object files):
--8<---------------cut here---------------start------------->8---
install-data-hook:
@$(am__vpath_adj_setup) \
list='$(nobase_mod_DATA)'; for p in $$list; do \
if test -f "$$p"; then d=; else d="$(srcdir)/"; fi; \
$(am__vpath_adj) \
echo " touch -r '$$d$$p' '$(DESTDIR)$(moddir)/$$f'"; \
touch -r "$$d$$p" "$(DESTDIR)$(moddir)/$$f"; \
done
@$(am__vpath_adj_setup) \
list='$(nobase_ccache_DATA)'; for p in $$list; do \
if test -f "$$p"; then d=; else d="$(srcdir)/"; fi; \
$(am__vpath_adj) \
echo " touch -r '$$d$$p' '$(DESTDIR)$(ccachedir)/$$f'"; \
touch -r "$$d$$p" "$(DESTDIR)$(ccachedir)/$$f"; \
done
--8<---------------cut here---------------end--------------->8---
IIUC it copies timestamps from $(srcdir) and $(builddir) to the
corresponding installed files.
It looks like this is all we need, right?
Problem is, each package that installs Guile object and source files
needs this hook...
Thanks,
Ludo’.
